Method of distilling petroleum under vacuum



Aug. 11, 1936. s. SJOHNSON. JR

7 METHOD. OF DISTILLING PETROLEUM UNDER VACUUM Filed Nov. 20, 1930 'Y i bohflSohAr, INVENTOR ATTONEYS Patented Aug. 11, 1936 UNITED STATES METHOD OF DISTIILING PETBOIiE UNDER VACUUM Stephens. Johnson, in, Short Hills, N. 1., as-

signor to The M. W.

Kellogg Company, New

York, N. Y., a corporation of. Delaware Application November 20, 1930, Serial No. 496,885 5 Claims. (01. 196-41) My invention relates to the distillation 01 oil and in particular to vacuum distillation of reduced stocks. A

In previous vacuum distillation operations it .5 has been the common practice to facilitate the distillation of heavy oils by the use of steam. Bythis means, it has been possible to-obtain' overhead cuts of heavy oils which otherwise are not obtainable. However, in using steam it has been 10 necessary to use large sized fractionating towers and other equipment and also a vacuum equipment of large capacity in order to take care of the immense increase in vapor volumes because of the steam. Not only has it been necessary to 15 increase the size and amount of the equipment with a resulting increase in expense, but it has also been necessary to increase the amount of cooling water and power used.

In order. to obtain proper fractionation it is, of course necessary to have a suitable reflux in the upper portion of the tower. Previously in vacuum distillation processes reflux has been added or returned which is substantially of. the same characteristics as condensate from the 25 vapors passing from the top of. the tower. This returned reflux is vaporized in the tower and further increases the total volume of vapor. This tends to decrease the fractionating eiiiciency of the -tower and necessitates larger equipment to 30 handle the vapors. 4 r

My process consists in removing the lighter products in a preliminary distillation under a. vacuum without the use of steam. I then fractionate under a high vacuum, the bottoms from 35 the first separation. In this second operation I may use some steam.

One of the primary objects of my invention is to overcome and eliminate the disadvantages outlined above. 3 e

A further object of my invention is to provide a method for vacuum distillation which does not necessitate excessively expensive or special equipment. I

Another object oi. my invention is. to .obtain 45 a vacuum distillation processfor reduced stocks in which at least a portion of the distillation may be carried on without the use of steam. v

" Another object is to provide a process in which an increased percentage of heavy stock may be 50 taken off overhead. e

- Another object is to provide a process by which a more complete fractionation and separation of the oil is provided. 4

Other objects and advantages of my invention 55 will become apparent from the following descrip- 33 to the barometric condenser'3l to which cooltion and drawing in which I have shown a dia grammatic outline of an apparatus whiclris suit able for carrying out my process.

Referring more particularly to the drawing in which like reference characters denote like 5 parts; the feed stock is drawn from a source of supply through line I by the charging pump '2 and is forced through the line 3 into the preheater or heat exchanger 4, from which it passes into the line 5 through the heat exchanger 6 and 10 q the line 1 into the heating tubes 8 and 8' inclosed in the refractory housing 9..- The heated products pass from the, pipe still through the line It into theli'ractionating tower II.' This portion of the iractionating tower extends down to the dividing section 12 which separates the upper part of the tower from the lower part. The upper fracv tionating tower H is fitted with fractionating sections or plates I3 having preferably, bellcap and downflow equipment, not shown. Vapors from the top 01' the tower pass ofi-through the line ll into the feed heat exchanger and partial condenser l and then through the line I5 into the total condenser IS. A cooling medium such as water may be admitted to the condenser I6 through the line I1 and discharged through the line l8. The liquid condensate is drawn oil? from the condenser through the line l9 and may pass into the accumulator 20 from which it may be drawn off by means of a pump 2| and forced through the line 22 to storage. Fixed gases and other uncondensed material are drawn ofl. from the condenser l6 through line 23 by means of the steam ejector. 24. superheated steam is passed into the ejector through the line 25. The

products are discharged from the ejector through the line 26 into the barometric condenser 21 to .which cooling water is admitted through the line 28 and the 'condensed'products and cooling water withdrawn through the line 29. Vapors are with- 4 drawn from this barometric condenser through the line 30 by the ejector 3| to whichsuperheated steam iaadmitted. through the line 32. The discharged products pass through the line ing water is admitted through the line 35 and from which the condensed products andcooling water are discharged through the line 36. The vapor remaining in the barometric condenser 34 is withdrawn through the line 31 by means of the ejector 38 into which steam is admitted through the line 39. The products from this ejector may be discharged through the line '40 to a steam well, not shown. Other suitable apparatus for maintaining a dry vacuum may be used of course, such as a dry vacuum pump.

Reflux condensate from the condenser I8 may be returned to the top of the tower ll through the line 4| and pump 42. This line is controlled by the valve 43. Reflux from an outside source may also be charged to the top of the tower through the line 4|, controlled by the valve 48'.

Liquid products may be withdrawn from several plates in the tower by means of the lines 44 and 45, and discharged to a stripping column 46 which may be fitted with stripping sections or plates 41 having preferably bellcap and downfiow equipment, not shown. Vapors from this stripping tower pass through the line 48 controlled by the valve 49 into the vapor line I4. They may also be discharged into the line 58 controlled by the valve 5| and thence into a condenser and heat exchanger 52 which is a unit of a secondary vacuum system which will 'be described more fully later. Steam may be admitted to the stripping tower 48 through the line 58. The liquid products from the stripping tower are withdrawn through the line 54 and pass through'the heat exchanger 8 to the cooler 55 from which they may be withdrawn by the pump 56 and passed to storage. Cooling liquid may be admitted to the cooler through line 55' and withdrawn through 55". Additional stripping drums may be used to withdraw other side streams if desired.

The bottoms from the first flash in the fractionating tower II are withdrawn through the has previously been described, this lower tower is separated from the upper fractionating tower II by means of the dividing section II. This tower is fitted at its lower portion with stripping sections or plates 82 having preferably the usual bellcap and downfiow equipment, not shown. The upper part of the tower is fitted with baffle plates 88. Steam may be admitted to the bottom of the tower through the line 84. The bottoms separated in this section are withdrawn through the line 85, through the cooler 88 and forced by means of the pump 81 to storage. Vapors from the fractionating tower 8| pass through the line 88 into the-condenser and heat exchanger. 52 to which cooling water is admitted through the line 88 and discharged through the line .10..- Con densate in this condenser may be returned to the upper fractionating tower II by means of the pump ll through the line H. Vapors are withdrawn from thecondenser and heat exchanger 52 through line I2 by means of the steam ejector 18 to which preferably superheated steam is admitted through the line 14 and the products discharged through the line 15 to the barometric condenser I8. Condensing water is admitted to this barometric condenser through the line 11 and the liquid products are discharged through the line 18. The remaining vapors are withdrawn through the line 18 by means of the steam ejector 88 to which steam is admitted through the line 8| and the products discharged through the line 82 into a barometric condenser 83. A condensing liquid is admitted to this barometric condenser through the line 84 and the products discharged through the line 85. The remaining vaporsare withdrawn through the line 88 by means of the steam ejector 81. to which steam is admitted through the line 88 and the products barometric condenser and two stage ejectors withv not shown. As stated before, any suitable type of equipment may be used to produce the desired vacuum.

The operation of my process is substantially as follows: 5

The charging stock, for example, reduced crude or other reduced stock is' drawn into the system through the line I by means of the charging pump 2 and forced through the line 3 into the preheater 4 in which it obtains a preliminary heat from the vapors being discharged from the top 'of the tower. The partially preheated stock is then forced through the line 5 into the exchanger 8 in which it picks up more heat from the lubricating oil out being withdrawn from the tower. The preheated stock which has been heated, for example, to a temperature of 400 F., then passes through the line 1 into the heating coils 8 and 8 of the pipe still. The feed stock is heated in the pipe stills up to a temperature, for example, of 20 650 to 700 F., andis discharged through the line l8 into the upper fractionating tower I I where it is flashed at an absolute pressure of between 30 and 40 millimeters. The vapors pass [upwards withdrawn through the line l4 to the condenser 4 where a partial condensation takes place due to the cooling action of the feed charging stock. The vapors and condensate then pass to the total condenser I 6 where further condensation takes place. The condensate is withdrawn, through the line I 9 and may pass to the accumulator 20 from which it is withdrawn by the pump 2| and forced to storage. This condensate under 35 ordinary conditions would be primarily gas oil and similar light. fractions. Fixed gases and other vapors are withdrawn from the condenser l6 through line 23 by means of the-steam ejector,

40 interbarometric condenser system previously described. The products from the last ejector 38 are discharged through the line 48 to the atmosphere or if it is desired they maybe discharged into a well.

Reflux from the condenser l8 may be returned to the top of the tower ll through the line 4| by means of the pump 42. If it is desired reflux may be drawn from some outside source and admitted to the system through the line 4|. Liquid products such as, for example, wax distillate or light cylinder stock may be withdrawn from the plates l3 of the fractionating tower ll through the lines 44 and 45. It is preferable that this withdrawn product be further fractionated to 5 strip it of any remaining light product and for this reason it is discharged into a stripping tower 46 in which further fractionation takes place. If

it is desired to facilitate the stripping action, steam may be admitted to the stripping tower 60 to the fractionating tower ll. These vapors may be discharged into the vacuum system connected to the fractionating tower 8|. No steam has been used in the first flash which takes place in the fractionating tower H and thus the vacuum system connected to the tower operates on what is commonly known as a dry vacuum. As will be later described the vacuum system connected to the tower 6| operates on a wet vacuum. The vapors from the stripping tower therefore may be discharged either to the wet or dry vacuum system depending upon whether steam is used in 75 the stripping tower or not. The liquid products are drawn off from the stripping tower by means of the line 54 and give up a portion of their heat forced by the pump 56 to storage.

- the cooler. 66 by means of in the heat exchanger 6 to the incoming feed. They are then further cooled in the cooler and The bottoms from the first flash in the fractionating tower I i in which the light ends for example, gas oil, wax distillate and light cylinder stock have been removed, are withdrawn through the line 51 by means of the pump 58. The temperature of the stock withdrawn from the bottom of the fractionating tower II will be approximately GOO-650 Ffand is reheated to a temperature of substantially 750 F., in the heating tubes 59 in the pipe still. The reheated stock is then disthe lower fractionating tower 6| for example,

charged into where it is flashed at a high vacuum,

'5-10 millimeters absolute pressure. The vapors pass upwardly around the baffle plate 63 and are withdrawn through the line 68 to the condenser 52. The condensate may be taken back through the line H into the upper fractionating tower ll.

' The vapors are withdrawn by means of the booster ejector I3, the two stage electors 80 and Hand the interbarometric condenser 83. The flnal vapors, fixed gases and steam may be discharged into a hot well.

The lower fractionating tower BI is fitted with stripping plates 62 which thoroughly strip the liquid portion of the second flash. This stripping may be facilitated by the ejection of steam through the line 64. The use of steam, of course, increases the volume of vapor, but due to the fact that the light ends have already been removed in the first flash and thus the vapor volume greatly reduced, it is possible to obtain an exceedingly high vacuum and a fine separation with less than the usual amount of steam. The products remaining liquid are withdrawn through the line and i the pump 61 and pass to storage. I

The condensate formed from the vapors in the condenser 52 may be returned through the line II to the upper iractionating tower II. This condensate of course, is of alower gravity than the reflux condensate which would be returned to the tower from the condenser It. At the temperatures present in the upper part of the tower II, the low gravity condensate will vaporize much less than the reflux from the condenser l6 and thus would not tend to increase the vapor volumes to an undesirable degree. The he'a condensate would act as a cooling medium wit n the tower and form reflux condensate therein, making it unnecessary to return a proportional amount ofreflux condensate from the condenser it. This,

of coursejs decidedly advantageous inasmuch .as it diminishes the vapor volumes within the tower and permits smaller and less expensive fractionating and vacuum equipment. I

Inasmuch as prior to the second flash in (the, tower ii the lighter ends have been removed, it is unnecessary to provide the usual 'belicap plate the drawing, I have merely insertedthe baiiles '83 in theupper part of the seoondfractionating tower. These serve to knock out liquid which is entrained in the vapors passing .into the line 83, and yet do not sufliciently constrict the now so stripping column or tower and thus that there is a back pressure formed. In my process by using a dry vacuum in a first flashing operation I am able to obtain a relatively high vacuum and yet use a fractionating tower of comparatively smalldiameter and a vacuum forming 5 equipment which is also of relatively small size. Furthermore, I am able to eliminate the expense of steam in the tower to facilitate distillation. Also due to the smaller vapor volumes 1 'am able to materially cut down the amount of power, 3 steam and cooling water necessary to effectively oarryon my vacuum producing operation. Due to the fact that I have already removed the light ends, I am enabled to obtain a very high vacuum in the second flash with a relatively small quantity of vapors to handle, and thus again I have materially reduced the size of fractionating equipment and vacuum equipment necessary to carry out the fractionation process. I

In a great many cases it is possible to have the 20 first fractionating tower and the second fractionating tower of the same diameter so that they may be placed one above the other as I have shown in my drawing. This, of course, adds to the compactness of the unit and further decreases the ex- 25 duces a large proportion of the necessary reflux 35 V within the tower as it passes downwardly through the plates ii to the lower plates where it may be withdrawn-through the lines 44 and 45 to the through the line 51 to the. reheater 59. I have thus been able to considerably reduce the vapor volume in the upper portion of the tower, and have therefore, overcapaa diiiicultyv which has been common in prior vacuum distillation equipment, namely, the tendency for excessive vapor velocities in the upper portion of the flashing tower wit a resulting reduction in the fractionating e ciency of the tower and furthermore, a tendency for the vapors to carry with them a considerable amount of entrained liquid to the condensing and vacuum producing equipment. The distillate which is withdrawn through the pipes 44 and 45 to the stripping column 46 may be further separated and fractionated in this column by the use of steam so that all light ends 5 are removed. It can be seen therefore, that notwithstanding the fact that I use a dry vacuum in the first flashing operation I am still enabled to obtain a secondary close separation of the desired product by means of the steam and without the use of separate processing equipment. As I .have described above, the vapors from this stripping column may be discharged .to either the wet or dry equipment depending on whether it is necessary to use steam'or not and otherfac- 6.) tors. By connecting the stripping column to the vacuum system for the second flash it may be possible to use a higher vacuum on the stripping less steam would be required. while I have shown and described.- only a speciflc process and form of apparatus, it is apparent to those skilled in the art that there are many Gil -modiflcations that may be made without departprocess described in the specification and drawing, but only by the appended claims.

What I claim is:

1. The method of distilling oil which comprises heating the oil, separating the heated oil into liquid and vapor and fractionating the resulting vapor under a low absolute pressure without steam, withdrawing the liquid residue from said separating step and reheating it, and separating said reheated liquid residue into liquid and vapor with the assistance of steam under a lower absolute pressure than said first separation.

2. The method of distilling oil which comprises heating the oil, separating the heated oil into liquid and vapor and fractionating the resulting vapor under a low absolute pressure without steam, withdrawing the liquid residue from said separating step and reheating it, separating said reheated liquid residue into liquid and vapor with the assistance of steam under a lower absolute pressure than said first separation, subjecting the liquid condensate formed in the first fractionat ing' to a stripping operation under vacuum with steam, and condensing the vapor from said stripping operation with the vapor from said second separation.

3. The method of separating lubricating oils from a topped crude oil which comprises heating the oil to an elevated temperature; passing the oil into a fractionating column, fractionating it therein while maintaining a substantial dry vacuum to produce lubricating oil fractions of intermediate boiling range and a heavy unvaporized fraction, withdrawing the latter and subjecting it without intermediate loss of heat to a further distillation under vacuum with the assistance of steam whereby heavier lubricating oil distillates of higher viscosity are obtained.

4. The method of separating lubricating oil irorn a topped crude oil which comprises subjecting the oil to successive steps each of which 5 comprises heating the oil while rapidly flowing in I a confined stream through a heating zone, im-

parting to the oil in that zone substantially all the heat needed for vaporization, discharging the heated oil into a separating chamber maintained under vacuum and separating the oil into a vapor and a residue; in one of said steps rectifying the vapor under a substantial dry vacuum to produce a rectified lubricating oil distillate of intermediate boiling range and viscosity; and in the succeeding step passing the heated oil countercurrent to a current of steam to vaporize lubricating oil of higher boiling range and viscosity.

5. The method of separating lubricating oil from a topped crude oil which comprises heating the oil while rapidly flowing in a confined stream through a heating zone, imparting to the oil in that zone substantially all the heat needed for vaporization, discharging the heated oil into a separating chamber maintained under vacuum 

